A phenolic OH-containing benzoxazine (F-ap), which cannot be directly synthesized from the condensation of bisphenol F, aminophenol, and formaldehyde by traditional procedures, has been successfully prepared in our alternative synthetic approach. F-ap was prepared by three steps including (a) condensation of 4-aminophenol and 5,5'-methylenebis(2-hydroxybenzaldehyde) (1), (b) reduction of the resulting imine linkage by sodium borohydride, and (c) ring closure condensation by formaldehyde. The key starting material, (1), was prepared from 2-hydroxybenzaldehyde and s-trioxane in the presence of sulfuric acid. F-ap is structurally similar to bis(3,4-dihydro-2H-3-phenyl-1,3-benzoxazinyl)methane (F-a, a commercial benzoxazine based on bisphenol F/aniline/formaldehyde) except for two phenolic OHs. The phenolic OHs can provide reaction sites with epoxy and 1,1'-(methylenedi-p-phenylene)bismaleimide (BMI). The structureproperty relationships between the thermosets of F-ap/epoxy, F-a/epoxy, F-ap/BMI, and F-a/BMI were discussed. Experimental data showed that thermosets based on F-ap/epoxy and F-ap/BMI provided much better thermal properties than those based on F-a/epoxy and F-a/BMI. (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 26862694